application.rb

module Whatsnext
  class Application < Sinatra::Base
    post '/features/*' do
      puts request.body.read
    end
  end
end

env.rb

require 'spec/expectations'
require 'rack/test'
require 'webrat'

Webrat.configure do |config|
  config.mode = :rack
end

class MyAppTest
  include Rack::Test::Methods
  include Webrat::Methods
  include Webrat::Matchers
  include Webrat::HaveTagMatcher
  
  def app
    Sinatra::Application
  end
end

steps.rb

When /^I save it as an existing file$/ do
  post("/foo", 'bar')
end